1713 - earliest extant clock. 1726 - first heard of the 1714 Longitude Act. 1735 - completed construction of his 'sea clock', H1. 1736 - sent on a voyage with H1 to determine the longitude of Lisbon. 1739 - after being awarded £500 by the Board of Longitude, completed construction of H2. 1749 - awarded the Copley gold medal by the Royal Society for his experimental work. 1759 - completed H3. 1760 - eventually produced his fourth timekeeper, the H4, the size of a large pocket watch. 1761 - H4 was sent on a trial to Jamaica.